The Colorado River — Tucson’s drinking water supply — carries nearly 20 percent less water than in 2000. Bark beetles are chomping away at our forests and killing off ponderosa pines. Wildfires are rapidly growing in intensity.

These problems have been linked to a drought that has stretched 19 years with no respite.

Now, a team of researchers concludes that the ongoing drought across the western U.S. rivals most past “megadroughts” dating as far back as 800 A.D. — and that this region is currently in a megadrought.

Using tree ring data as a proxy for drought conditions, the researchers say the current drought ranks fourth worst among comparable 19-year periods of megadroughts of the past 1,200 years.

A significant factor in this ranking is global warming triggered by human-caused climate change, says Park Williams, the study’s lead author and an associate research professor at Columbia University’s Lamont-Doherty Earth Observatory.

“The drought severity of the last 19 years is almost as bad as the worst 19-year period of the worst megadrought. It indicates that it’s very important that we develop more sustainable ways of dealing with water and allocating water across the western U.S.,” Williams said in a blog posted by Columbia’s Earth Institute…

The idea that this drought is among the worst compared to past megadroughts draws support from other researchers. There’s disagreement, however, as to whether the West is actually in a megadrought now.

It’s going to take more drought years before researchers Connie Woodhouse of the University of Arizona and Toby Ault of Cornell University — who also have studied megadroughts — are willing to use that term this go-around.

Ault’s threshold for a megadrought is 35 years, although he acknowledges that many researchers use 20 years. Woodhouse, a tree ring researcher who co-authored a pioneering study on megadroughts 20 years ago, said she hasn’t used a specific period to define megadroughts but that this drought hasn’t lasted long enough to qualify.

“The definition of megadrought technically is open to debate,” Jonathan Overpeck recently told The Atlantic in an article on Williams’ study. Overpeck is a University of Michigan climate scientist who formerly ran UA’s Institute for the Environment.

“The drought in the Southwest is right on the cusp of technically being a megadrought,” said Overpeck, who co-authored the 1998 study with Woodhouse and gets credit from her for coining the term…

One difference between this drought and most past megadroughts is that this one’s effects have been spread over the entire West, whereas the earlier droughts were more heavily concentrated in parts of the region, Williams told the conference.

Not a lot of places in the West are experiencing their worst droughts on record today, “but instead, a lot of places are experiencing pretty severe droughts,” Williams said.

Today’s drought pattern could have the fingerprints of human-caused climate change, he said. By using computer-based climate models, the Columbia researchers calculated that climate change has made the current drought 38 percent more severe…

Either way, the study said, “Water managers in the Southwest should plan for the possibility of a megadrought before the end of this century.”